This invention relates to a hydrostatic transmission. More specifically, this invention relates to a self-actuating clutch assembly within a hydrostatic transmission that improves clutching efficiency.
There are a number of vehicles that have automatic transmissions for ease of driving in increased utility. These include ATVs, tractors and utility work vehicles. These vehicles have common requirements for low cost, high efficiency, good control ability, and continuous ratio change throughout the entire speed range. Hydromechanical transmissions have utility in these vehicles because they meet these needs and can be designed with compact size.
Hydromechanical transmissions are characterized by a hydrostatic transmission power path in parallel with a mechanical power path that is arranged in a manner to decrease the average power flow from the hydrostatic portion and thereby increase operating efficiency. The existence of the parallel power path creates the possibility of reducing the output speed range or torque ratio in order to further reduce transmitted hydrostatic power. This requires multiple ranges or “modes” to achieve the full torque and speed range of the transmission.
Multi mode hydromechanical transmissions (HMTs) are usually accomplished by reusing the hydrostatic components and clutching to a different mechanical component. Usually the gearing is arranged so that there is no ratio change during the mode change, or clutching process, in order to have continuous speed and torque delivery. During a mode change, one clutch is exchanged for another at a near synchronous speed. The clutch differential speed is ideally pre-synchronous in order to have the fastest and smoothest shifts.
Previously, two or three mode hydromechanical transmissions have been provided that use mechanical dog clutches having mating slots and tangs. These dog clutches are low cost and compact and are actuated with a simple, low force mechanical system. However, there are some operating conditions where engaging the clutches under dynamic conditions is a problem as dog clutches will not allow any slipping during engagement. Other solutions provide two or three mode hydromechanical transmissions with several coaxial clutches which are in a multiple disc configuration. Multiple disc clutches are usually designed to allow some slippage during engagement thereby easing the synchronizing process but adding cost and size to the transmission. Multiple disk clutches require a high actuating force, a complex actuating system and normally require oil flow to cool the discs and reduce disc flutter.
Thus, it is the primary object of the present invention to provide a hydromechanical transmission that provides a cost effective clutching mechanism.
Yet another object of the present invention is to provide a hydromechanical transmission that provides a more efficient clutching mechanism.
Another object of the present invention is to provide a clutch mechanism that allows slippage during engagement to improve the operation of a hydromechanical transmission.
These and other objects, features, or advantages of the present invention will become apparent from the specification and claims.